Wash buttercup pumpkin, cut in half and remove seeds, then slice into even sized wedges. Arrange on an oven tray.
In a small dish, mix together olive oil, garlic, rosemary, chilli, orange zest and juice. Pour over the pumpkin, then use your hands to rub the mixture over all surfaces. Season with salt and a good grind of black pepper.
Roast pumpkin for approximately 30 minutes (turn after 20 minutes), until the flesh is tender and the skin and edges are caramelised.
For the sauce, stir all ingredients together until smooth. Taste and adjust seasoning if necessary.
Serve roast pumpkin hot from the oven, with a dollop of yoghurt tahini sauce.
Nutrition information estimate based on six servings.
Adjust quantity of chilli to suit your taste - one chilli provides a warm hum, two chillis will kick it up a notch.